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Optical signal attenuation caused by a flow field has been examined using a Malley Probe and compared to a low-turbulence, compressible flow of M = 0.6 over a backward facing step reference case.

Three completely different turbulence configurations were generated by the manipulation of the boundary layer prior to flow separation over the step using a fence, spire, and artificial roughness combination. (The three boundary layer conditions at the step edge are shown below.)

Each of these flow conditions affects the propagation of coherent light beams through the medium and can alter the optical characterization of a communications, sensing and threat neutralization system due to optical wave-front aberration.

The Optical Path Difference (OPD) measurements show the effect of vortical scales on signal attenuation for the three flow configurations, and are subsequently presented in terms of a Strehl ratio for air flowing at Mach 0.6 and separating at the edge of the backward facing step.

Strehl Ratio Plot Optical Path Difference
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